This invention relates to a polyphenylene sulfide resin composition, and to a resin-encapsulated semiconductor device manufactured by making use of the polyphenylene sulfide resin composition.
Almost all kinds of resin-encapsulated semiconductor devices are now sealed by making use of a transfer molding method. According to the transfer molding method, an uncured resin tablet such as epoxy resin molding material consisting mainly of epoxy resin containing phenol novolak resin as a curing agent and a filler is heated to melt at first, and then the resultant melt is poured into a mold by making use of a transfer molding machine, thereby allowing the melt to be cured under a high temperature and high pressure condition, thus obtaining a resin-encapsulated semiconductor device where a semiconductor chip mounted on a lead frame for instance is sealed with a resin composition. The resin-encapsulated semiconductor device manufactured in this manner is excellent in reliability because the semiconductor chip is completely sealed and also excellent in the outer appearance thereof as a package because it is densely molded by making use of a mold. In addition to this transfer molding method, there are known an injection molding method employing a thermoplastic resin and a potting method employing a liquid sealing resin, which are now actually employed in the manufacture of a resin-encapsulated semiconductor device.
Meanwhile, in a recent trend to enlarge the dimension of a semiconductor chip in compliance with an increasing integration density of semiconductor device, the requisites demanded of a resin to be employed for encapsulating a semiconductor device has become increasingly severe. There are also demands for a development of material which is pollution-free or unharmful to environments and suited for improving the productivity of a resin-encapsulated semiconductor device, and for a development of a molding method which is capable of minimizing the production of useless portions such as cull and runner. Furthermore, there are also demands for a development of a recyclable sealing material, or for a development of a sealing material which is excellent in storage stability.
Generally, an epoxy resin-based sealing material contains as a flame retardant a halogen compound or antimony trioxide. Furthermore, the ordinary epoxy resin-based sealing material also contains a large amount of a curing agent with a view of improving the productivity thereof. However, due to the inclusion of these additives, the ordinary epoxy resin is poor in storage stability. Since the addition of a flame retardant such as halogen compound is not desirable because of the reason as mentioned above, it is now studied to develop an epoxy resin-based sealing material where these materials would be incorporated in a lesser amount or would not be incorporated at all, or to develop a latent catalyst which is excellent in storage stability.
In order to ensure the flame retardency of epoxy resin-based sealing material without incorporating a flame retardant, the content of a filler may be required to be increased. Under the circumstances, it has been studied to find out a filler exhibiting an excellent fluidity or a resin of low viscosity. However, most of these attempts have failed to put them into practical use, since the employment of such a filler or resin would lead to a deterioration of moldability. Accordingly, it has become difficult to employ an epoxy resin-based sealing material while meeting the aforementioned severe demands of today.
On the other hand, the employment of thermoplastic resin such as PPS (polyphenylene sulfide) resin and liquid crystal polymer is now studied. Although these thermoplastic resins are excellent in storage stability and flame retardency, the viscosity thereof is relatively high, so that various problems would be raised when these thermoplastic resins are employed for encapsulating a semiconductor element. Specifically, bonding wires may be excessively deformed so that a phenomenon such as a dislocation of bed may be caused. Moreover, since these thermoplastic resins are poor in adhesivity to a metal member to be encapsulated, such as a 42 alloy frame, a Cu frame or a semiconductor chip, it has been difficult to manufacture a semiconductor device having a sufficient moisture resistance. In particular, when the encapsulation of a semiconductor device is performed by making use of a PPS resin, the resultant encapsulated semiconductor device may become poor in ductility thus making it fragile, so that it is impossible to obtain a sufficient strength and toughness which are desired of a resin composition for encapsulating a semiconductor element. In an attempt to overcome this problem, the employment of a PPS resin which is low in molecular weight and in viscosity, and contains a large amount of a filler is now studied. However, since this sealing resin is low in molecular weight, it would be impossible to obtain a sufficient mechanical strength after the curing thereof, and, due to this fragility, the resultant package may be destroyed at the occasion of ejecting it from a mold. It is also studied to employ various additives for the purpose of improving the adhesivity of the PPS resin. However, there is a problem that the employment of these additives may damage the inherent characteristics of the PPS resin such as flame retardency.
Moreover, the synthesis of PPS resin may accompany a production of ionic impurities such as Na and Cl as a side reaction product. If these impurities are left remained in a resin composition, they would badly affect the reliability of the resultant semiconductor device. Therefore, various methods have been tried to wash out or remove these ionic impurities. However, the resin composition which has been subjected to a treatment to remove these ionic impurities by the conventional method becomes poor in adhesivity to a metal such as a lead frame, so that water may be penetrated into an interface between the resin and a lead frame thereby to deteriorate the reliability of semiconductor device. A coupling treatment of a lead frame or a method of coating an epoxy type adhesive on a lead frame may be effective to solve this problem. However, even if these treatments are employed, it is still difficult to obtain a satisfactory product which is capable of withstanding a high temperature and high humidity condition. Furthermore, the employment of these treatments are not preferable in view of simplifying the process and enhancing the productivity.
As explained above, the employment of an epoxy resin-base sealing material is accompanied with various problems such as poor storage stability. On the other hand, it has been difficult in the employment of a PPS resin to realize an excellent moldability and a sufficient strength though the PPS resin is excellent in storage stability and flame retargency.